Hot melt adhesives are widely used for various commercial applications such as product assembly and packaging, including case sealing and carton closing operations. Such hot melt adhesives are applied to a substrate while in its molten state and cooled to harden the adhesive layer.
Most commercially available hot melt adhesives require temperatures of 350° F. (177° C.) or greater to ensure complete melting of all the components and also to achieve a satisfactory application viscosity. The need for such elevated temperatures is not without problems. The high temperatures increase operator risks with respect both to burns and to inhalation of residual volatiles. In addition, use of high temperatures require more energy, placing greater demands on the manufacturing facility. While adhesive formulations that can be applied at temperatures below 300° F. (151° C.) can be prepared using low molecular weight components or a high wax content, application viscosity may suffer and there is a loss of adhesive properties, e.g., toughness, heat resistance and, often, specific adhesion to a substrate. While softer or more amorphous components may be added in order to improve adhesion, these components reduce the effective heat resistance.
There continues to be a need in the art for improved hot melt adhesives that can be applied at temperatures of from about 100° C. to about 135° C., have good bond strength with exceptional toughness, good heat resistance and acceptable application viscosity, even when prepared with relatively low molecular weight components. The current invention fulfills this need.